The wireless industry has grown at a tremendous pace over the past few years. Wireless communication has become a standard part of every day life. Most people utilize some variant form of wireless communications such as Global System for Mobile communication (GSM), Universal Mobile Telecommunications System (UMTS), Carrier Detection Multiple Access (CDMA) and 802.11 in various aspects of daily living.
Generally, radio systems are designed for a certain area of coverage or footprint. These areas are generally referred to as cells. Cells enable the reuse of similar frequencies by multiple sources to support services in metropolitan areas that are some distance apart. The geographic size of cells are not necessarily consistent throughout a given area and may vary due to frequency and power level, topography of the area, time of day and so forth. Communications within these cells take advantage of a concept known as Demand Assigned Multiple Access (DAMA). DAMA enables multiple devices to access a network in a shared manner on a demand basis. Basically, devices access the network on a first come, first serve basis. Within a wireless network, there are a number of ways in which multiple access can be provided to end-users. At the most basic level, there is a Frequency Division Multiple Access (FDMA) methodology, which is essentially the starting point for all wireless communications, given that each cell must be separated by frequencies to avoid interferences among wireless devices. FDMA divides assigned frequency ranges into multiple carrier frequencies in order to support multiple conversations.
Another method that is utilized in wireless networking is the Time Division Multiple Access (TDMA), which is a digital technique that divides each frequency channel into multiple time slots. Each of the time slots within a frequency channel supports an individual device conversation. Generally speaking, services based on TDMA offer roughly three times the traffic capacity of FDMA services.
Yet another communication methodology which is relatively new and has its root in spread spectrum radio is known as Code Division Multiple Access (CDMA). Spread spectrum radio spreads the bandwidth of a transmitted signal over a spectrum of radio frequencies. The combined spectrum of radio frequencies is usually much wider than what is required to support the narrow band transmission of the signal. Spread spectrum uses two techniques namely, Direct Sequence (DS) and Frequency Hopping (FH). In brief, direct sequence spread spectrum is a packet radio technique in which the narrow band signal is spread across a wider carrier frequency band. In other words, the signal information is organized into packets, each of which is transmitted across a wider carrier band frequency in a redundant manner i.e. packets are sent more than once. Multiple transmissions can then be supported. The transmissions from specific terminals are identified by a unique code such as, a 10 bit code that is pre-pended to each data packet. Frequency Hopping Spread Spectrum is generally preferred over direct sequence spread spectrum. FHSS involves transmission of short bursts of packets within the wide band carrier over a range of frequencies. Essentially, the transmitter and receiver hop from one frequency to another in a choreographed hop sequence and a number of packets are sent to each frequency. The hop sequence is controlled by a centralized base station antennae.
Regardless of the communication methodology for a given network, a certain amount of pre-configured set-up and real time set-up of communication devices will be required. One such requirement for communication between a remote/mobile unit and a base station is the set-up and configuration of certain communication parameters. For example, with packet data mode communications data rate, availability and maximum delay time for each packet communication must be set-up and negotiated between the remote unit and the base. Generally, this negotiation and configuration occurs in real time at the moment when the remote unit first initiates a communication session with the base station. Since every remote unit must access the base station, there is typically an overloading of the network particularly in large metropolitan areas. This results in an inability or at best a long delay for some remote units, which is problematic for emergency type units or dispatch units.
The availability of a method to provide access to certain remote units such as dispatch units, emergency personnel units and so on is required. The importance of improving access time can be quite dramatic depending on the mobile unit application. For instance, a dispatch unit that needs to communicate with multiple mobile units would benefit greatly from improved access to the targets. As such, there exists a need to provide a system and method to reduce the delay for time critical communications between an initiating mobile unit and other target mobile units.